The invention relates to a semiconductor device and a semiconductor apparatus. In particular, the invention relates to a semiconductor device mounted on a mounting member with adhesive or solder, and a semiconductor apparatus equipped with such a semiconductor device.
Semiconductor devices often require compatibility between miniaturization and heat dissipation. For example, in recent years, it is important in the field of mobile communication including cellular phones to enhance the performance of high-frequency semiconductor power devices used in the transmitting unit. More specifically, these semiconductor power devices require not only a good high-frequency performance, but also a good heat dissipation because a device of only several millimeters square has power consumption up to several watts. In other words, the heat resistance of the semiconductor device must also be reduced.
Semiconductor devices are mounted on, for example, a circuit board. The mounting area of a semiconductor device is determined by a method of bonding the semiconductor device onto the board. There are various methods of bonding the semiconductor device onto the board. Typical methods include those using solder, silver paste or epoxy-based adhesives.
FIG. 23 is a schematic view showing a cross-sectional structure of a semiconductor apparatus that the inventor investigated in the process of reaching the invention. The semiconductor apparatus 200 has a mounting board 107 and a semiconductor device 100 mounted thereon. The semiconductor device 100 has a GaAs substrate 102, a HBT (heterojunction bipolar transistor) device section 104 formed on the GaAs substrate 102, a polyimide insulating protection film 103 for protecting the HBT device section 104, and bonding gold (Au) pads 105 formed on the GaAs substrate 102. The HBT device section 104 is formed by epitaxial growth on the GaAs substrate 102. When the semiconductor device 100 is mounted on the mounting board 107, a certain amount of adhesive or solder 109 is first applied to the surface of the mounting board 107. The semiconductor device 100 is then placed on the adhesive 109, and bonded to the mounting board 107 by pressure from above or by descending of its own weight. Subsequently, the bonding pad 105 on the semiconductor device 100 is electrically connected with a bonding Au pad 108 on the mounting board 107 via a bonding wire 110.
In a structure of soldering a semiconductor device onto aboard as described above, it is also proposed that a peripheral portion of the bottom surface of the semiconductor device is notched to provide a connection strengthening space for thickening the solder layer (Japanese Laid-Open Patent Application (Kokai) H06-177178).
However, these semiconductor apparatuses have a problem that an excess of adhesive 109 is pushed out around the semiconductor device 100 when the semiconductor device 100 is mounted on the mounting board 107.
More specifically, when the semiconductor device 100 is placed on the adhesive 109 and bonded to the mounting board 107 as described above, an excess of adhesive (solder) 109 is discharged around the semiconductor device 100. This process can improve adhesion between the semiconductor device 100 and the mounting board 107 and reduce the film thickness of the adhesive (solder) 109 under the semiconductor device 100. As a result, the heat resistance of the semiconductor apparatus can be decreased.
However, the excess adhesive 109 discharged around the semiconductor device 100 extends from the side surface of the semiconductor device 100 to its periphery. The inventor's investigation has found that the associated distance D2 may exceed 0.4 mm. Because of this “squeezeout” of adhesive 109, the distance between the semiconductor device 100 and the bonding pad 180 of the mounting board 107 is forced to be increased, which inevitably also lengthens the bonding wire 110. The lengthening of the bonding wire 110 increases its parasite inductance, which degrades the high-frequency characteristics of the semiconductor apparatus. This is undesirable for adapting the semiconductor apparatus to high frequencies. In addition, the squeeze out of adhesive 109 also increases the overall area of the mounting board for the semiconductor device, which is also undesirable for miniaturization of the semiconductor apparatus. In other words, there is a need for decreasing the area of adhesive squeezeout around the semiconductor device.
Similar problems also occur in the semiconductor device disclosed in Patent Document 1. More specifically, even if a peripheral portion of the bottom surface of the semiconductor device is notched, the inside wide region of the bottom surface is flat. The solder applied to the region is thus discharged to the periphery to cause “squeezeout”.